At least 60 people have been killed in a bloody prison riot in the Amazon city of Manaus in Brazil.

Authorities said the riot was sparked by a war between rival drug gangs with a number of inmates having made their escape during the violence.

The head of security for Amazonas state, Sergio Fontes, told a news conference that the death toll could rise as authorities get a clearer idea of the scale of the rebellion - with reports that decapitated dead bodies were thrown over the prison walls.

Mr Fontes said the “biggest prison massacre” in the Amazon state’s history began late on Sunday and was brought under control by around 7am on Monday.

The riot ended after the inmates freed the last of the 12 prison staffers they had held hostage.

Brazil has been the subject of heavy international criticism over the years due to the conditions within its jail system - which are often heavily overcrowded.

Reuters reports that the massacre may have been the result of ongoing clashes between inmates aligned with the Sao Paulo-based First Capital Command (PCC) drug gang - Brazil's most powerful - and a local Manaus criminal group known as the North Family.

The Manaus-based gang is widely believed to be attacking PCC inmates at the behest of the Rio de Janeiro-based Red Command (CV) drug gang, Brazil's second largest.

Security analysts have said that a truce that held for years between the PCC and CV was broken last year, resulting in months of deadly prison battles between the gangs and sparking fears that chaos will spread to other prisons.